The proper spacial and temporal development of the vasculature may be a critical event in the normal development of an organism and its component organs. Our work aims at studying the contributions of the vasculature to the normal "differentiation" of various tissues. Furthermore, because endothelial cells demonstrate a type of "controlled" invasiveness we are studying proteolytic activities of endothelial cells which may be operative in the process of invasion. Using as models tissues that do not vascularize, such as cartilage, we are determining which are the factors operative in these tissues that prevent endothelial cell invasion. In cartilage there seem to be two different factors which are responsible for the inhibition of invasion by endothelial cells. These two factors are small polypeptide which are now being isolated. BIBLIOGRAPHIC REFERENCES: Cell-surface-associated and released proteolytic activities of bovine aorta endothelial cells. Zoltan Tokes and Nino Sorgente. Biochem. Biophys. Res. Comm. 73:965-971, 1976. Basal lamina degradation: The identification of mammalian-like collagenase activity in mesenchymal-derived matrix vesicles. Nino Sorgente, Anna G. Brownell, and Harold C. Slavkin. Biochem. Biophys. Res. Comm. 74: 448-454, 1977.